MIMO communication systems offer large increases in throughput due to their ability to support multiple parallel data streams that are each transmitted from different antennas. In single user MIMO (SU-MIMO), a user is served by one base station, and the user occupies a transmission resource, such as time or frequency, exclusively. SU-MIMO requires that the user has multiple transmit antennas and receive antennas. An objective of the protocol is to increase the data rate and communication reliability by exploiting the spatial multiplexing gain or spatial diversity gain available in MIMO channels.
In the most general form, MIMO transmissions employ a number of parallel spatial streams that are independently forward error correction (FEC) encoded. Each stream, also termed a codeword associated with a transport block, is then mapped to one or more spatial transmission layers. Mapping to multiple antennas can be done by introducing a linear transformation from the transmission layers to the physical antennas. The number of spatial transmission layers is called the rank of transmission, and the layers are mapped to the physical transmit antennas. This mapping is typically accomplished by linearly combining the layer signals to obtain the actual transmit signals. This operation is also termed pre-coding. A pre-coding matrix can be selected from a pre-determined set of matrices called a codebook. In such a case, the pre-coding operation is termed codebook-based pre-coding. It is also possible to perform non-codebook-based pre-coding. Overall, codebook-based signaling tends to require less signaling overhead.
Although current MIMO communications offer advantages over single antenna systems, further improvements would prove beneficial in the art.